The Bulletin is published weekly during the academic year,
except during University breaks and exam weeks, by the Office of Communications.
Second class postage paid at Princeton. Postmaster: Send address changes to
Princeton Weekly Bulletin, Office of Communications, Princeton University,
22 Chambers St., Suite 201, Princeton, NJ 08542. Permission is given to adapt,
reprint or excerpt material from the Bulletin for use in other media.

Subscriptions. The Bulletin is distributed free to faculty,
staff and students. Others may subscribe to the Bulletin for $30 for the 2005-06 academic year
(half price for current Princeton parents and people over 65). Send a check to Office of
Communications, Princeton University, 22 Chambers St., Suite 201, Princeton, NJ 08542.

Deadlines. In general, the copy deadline for each issue is
the Friday 10 days in advance of the Monday cover date. The deadline for the Bulletin
that covers Nov. 7-13 is Friday, Oct. 28. A complete publication schedule is available at
publication schedule
or by calling (609) 258-3601.

Princeton NJ—A discovery by Princeton researchers may lead to an
efficient method for controlling the transmission of light and improve new
generations of communications technologies powered by light rather than
electricity.

Princeton researchers tested whether quasicrystals—an unusual form
of solid—would be useful for controlling the path of light by constructing a
three-dimensional, softball-sized model of such a structure with 4,000
centimeter-long polymer rods. (Courtesy of Paul Steinhardt)

The discovery could be used to develop new structures that would
work in the same fashion as an elbow joint in plumbing by enabling light to
make sharp turns as it travels through photonic circuits. Fiber-optic cables
currently used in computers, televisions and other devices can transport light
rapidly and efficiently, but cannot bend at sharp angles. Information in the
light pulses has to be converted back into cumbersome electrical signals before
they can be sorted and redirected to their proper destinations.

In an experiment detailed in the Aug. 18 issue of Nature, the
researchers constructed a three-dimensional model of a quasicrystal made from
polymer rods to test whether such structures are useful for controlling the
path of light. A quasicrystal is an unusual form of solid composed of two
building blocks, or groups of atoms, that repeat regularly throughout the
structure with two different spacings. Ordinary crystals are made from a single
building block that repeats with all equal spacings. The difference enables
quasicrystals to have more spherical symmetries that are impossible for
crystals.

Ordinary crystals had been considered the best structure for making
junctions in photonic circuits. But the researchers proved for the first time
that quasicrystal structures are better for trapping and redirecting light
because their structure is more nearly spherical. Their model, which had the
same symmetry as a soccer ball, showed that the quasicrystal design could block
light from escaping no matter which direction it traveled.

The finding represents an advance for the burgeoning field of
photonics—in which light replaces electricity as a means for transmitting and
processing information—and could lead to the development of faster
telecommunications and computing devices.

“The search for a structure that blocks the passage of light in all
directions has fascinated physicists and engineers for the past two decades,”
said Princeton physicist Paul Steinhardt, a co-author of the Nature paper, who
invented the concept of quasicrystals with his student Dov Levine at the
University of Pennsylvania in 1984.

“Controlled light can be directed, switched and processed like
electrons in an electronic circuit, and such photonic devices have many
applications in research and in communications,” Steinhardt noted.

Co-author Paul Chaikin, a former Princeton professor now at the
Center for Soft Matter Research at New York University, said, “Ultimately,
photonics is a better method for channeling information than electronics—it
consumes less energy and it’s faster.”

The paper’s other co-authors are Weining Man, who worked on the
project as part of her doctoral thesis in Princeton’s physics department, and
Mischa Megens, a researcher at Philips Research Laboratories in the
Netherlands.

To conduct their experiment, the researchers constructed the
world’s first model of a three-dimensional photonic quasicrystal, which was a
little larger than a softball and made from 4,000 centimeter-long polymer rods.
They observed how microwaves were blocked at certain angles in order to gauge
how well the structure would control light passing through it.

Building the physical model was a breakthrough that proved more
valuable than using complex mathematical calculations, which had been a hurdle
in previous efforts to evaluate the effectiveness of photonic quasicrystals in
blocking light.

“The pattern in which photons are blocked or not blocked had never
really been computed,” Steinhardt said. “In the laboratory, we were able to
construct a device that was effectively like doing a computer simulation to see
the patterns of transmission.”

Chaikin added, “We showed that it has practical applications, and
we also found out some properties of quasicrystals that we didn’t know before.”

The researchers are now
exploring ways of miniaturizing the structure in order to utilize the device
with visible light instead of microwaves. They also are examining whether the
quasicrystal designs may be useful in electronic and acoustic applications.